The present invention relates to a hydrofoil boat stabilizer having a true lifting airfoil/hydrofoil shape incorporated into the design, which provides lift to the stern of the boat. The hydrofoil boat stabilizer is attachable to a cavitation plate on the lower drive unit of a boat motor.
The skilled artisan understands that the drive system of a boat generates the forward thrust. The same skilled artisan also understands that the boat and drive system are fighting the forces of drag upon the boat as it rides low in the water. Thus, the higher in the water, or “on the plane,” a boat rides, the less drag it encounters. Therefore, it is desirable to reduce the amount of boat drag.
Boats inherently have drag from many sources, and one way to reduce drag is to get the boat on the plane faster by providing lift to the lower drive unit with a boat stabilizer. Unfortunately, while providing lift and reducing drag on the boat, these same stabilizers also introduce additional drag, limiting the overall performance of the boat and motor.
In their attempt to manage water flow, the designers of the known boat stabilizers inadvertently introduce one or more points of cavitation in and around the stabilizer by choosing a design that is not a true hydrofoil shape, or by choosing the wrong true hydrofoil shape for the application. As the speed of the boat varies, the position of the cavitating water changes location on the stabilizer and often increases in magnitude. Cavitation is the rapid formation and collapse of vapor pockets in moving water in regions of very low pressure. Accordingly, cavitation is controlled on the hydrofoil by keeping the maximum velocity that occurs on the hydrofoil below the limit at which cavitation occurs, or has significant effect. This cavitation of the water introduces significant levels of drag.
It is desirable to have the “right” true hydrofoil shape for a boat stabilizer. A true hydrofoil shape is a hydrofoil designed and tested by using aerodynamic/hydrodynamic design principles and procedures, such as the foil design software, XFOIL Subsonic Airfoil Development System, from the Massachusetts Institute of Technology, or a similar such program. A true hydrofoil shape improves performance, and reduces both cavitation and drag. Various hydrofoil designers have produced and tested several true hydrofoil shapes, each having different performance characteristics across a wide range of performance parameters at differing speeds, to include lift, drag, profile drag, cavitation, and laminar-to-turbulent transition. Some non-limiting examples of hydrofoil shapes include the NACA 63-209, Eppler E817, Eppler E818, Eppler E836, Eppler 837, Eppler E838, Eppler E874, Eppler E904, Eppler E908, and the Speers H105. The “right” true hydrofoil shape is one that is applicable for the particular performance characteristics desired for the boat, engine and boat stabilizer. For example, a performance characteristic might be a constant, total laminar flow across the entire hydrofoil wing section for a given speed range.
Hydrofoil lift characteristics are balanced against drag and cavitation resistance for given speeds. Preferably, the hydrofoil will control cavitation across a broad range of speeds/velocities. One example of hydrofoil performance is the H105 hydrofoil shape, which has a profile drag that is nearly constant as the laminar-to-turbulent transition point moves forward on the upper surface of the hydrofoil. Simultaneously, the laminar-to-turbulent transition point moves aft on the lower surface as flow speed increases. This results in the example H105 hydrofoil maintaining nearly the same total amount of laminar flow across it, thereby providing strong lift characteristics. By maintaining a constant laminar flow, the rapid formation and collapse of vapor pockets along the hydrofoil are reduced to a constant level, thereby reducing the opportunity for creation of additional drag due to cavitation.
A need exists for a boat stabilizer that has a true hydrofoil shape, low-drag and minimizes cavitation on and around it. Additionally, a need exists for a hydrofoil boat stabilizer that provides good lift characteristics to minimize drag and cavitation.